How are you converting V-Log to "normal" colour?

[hyalinejim]

As I was watching the S5II reviews I realised that people are taking the same V-Log files and ending up with very different colour results. I guess there are four main approaches - use the colour in the file untouched, use Panny's LUT, use Resolve's Rec709 conversion, or use a third party LUT. This post compares the accuracy of each and discusses the trade-offs that might be made. This applies to the GH6 and any other Panasonic cameras that share a similar color palette.

I'll be using extracted colour patches from a colour target. This is how the chart looks in reality:

Below, I match the gamma of a GH6 V-Log shot of this chart and then look at the results. Open in paired tabs on a monitor and flick back and forth to compare.

 

1. Don't transform the colour, just add contrast:

You can see here by comparing with the original that overall saturation is way down, cyan magenta and yellow are too bright, reds are too orange, greens are too yellow and blues are too bright. Skintones are too green. I guess some people grade like this. However the colours are still in V-gamut and ideally should be transformed to Rec709. Even when I manually colour grade in Resolve so that some patches are accurate, then others are still totally off. Not recommended.

 

2. Use Panasonic's VLog to V709 LUT

This official LUT comes with a half-assed curve as part of it. But you can separate the components using LutCalc and just get a LUT that is the colour transform only. The colour LUT must come first, before the curve, or things will go wonky.

Cyans are too bright, magentas too pale, yellows too dark and orangey, reds a smidgen too bright and orangey, greens too pale and light, and blues are absolutely far too light and cyan. Skintones are slightly too pink.

Despite these colour inaccuracies this is actually a good colour transform in the sense that as far as I have looked I have never spotted any colour weirdness in the image like banding or colour clipping. It's a slightly muted look though, and not good for landscapes - foliage, sea and sky will suffer a washed out fate here.

 

3. Use Resolve's Color Space Transform to convert to Rec709 colour

Note that Panasonic's official LUT is available in Resolve under the LUT menu. However, you will get different colour results using the Color Space Transform effect to convert V-gamut to Rec709. I was a little bit excited when I saw these results at first. It looked off-hand to be a bit better than Panny's conversion, especially in terms of the lightness of the blues. However closer inspection reveals that although cyans are just about right, magentas are too bright and saturated, yellows too orange, reds too bright and saturated, greens are close but deep blues are oversaturated.

This colour conversion differs from the Panny insofar as it has to be applied after the curve conversion, not before. When you do this I noticed some weird colour artifacts in footage I'd shot at an aquarium. So yes, the blues are more accurate but the inaccurate Panny conversion gave an image with integrity whereas blues began to clip and go weird (even with saturation mapping).

Overall, this gives more accurate and I think nicer colour than Panny. However, if I was a wedding or nightclub shooter I'd be wary of colour artifacting in strong coloured lighting scenarios.

 

4. Third party LUT

I was interested to see if I could make a colour accurate LUT for the GH6. I gave it a go and you can check out the LUT here. The LUT must go after the contrast curve, not before!

Yes, it's very accurate compared to the other approaches. When contrast is relatively moderate and the range of colours is not so saturated it looks a bit similar to the Resolve transform. However, there is much better hue accuracy and saturation control in all tonal areas, which you really notice if you crank up the contrast or have very saturated. However, I did still notice some of that colour weirdness in the aquarium shots. So it looks like Panasonic know what they're doing in terms of sacrificing colour accuracy to preserve image integrity. And I guess if total colour accuracy is what you're after you need to shoot RAW!

Finally, here's a comparison on a real world image:

Vgamut

 

Panasonic Vgamut to V709

 

Resolve Vgamut to Rec709 (skintones are nice but note the oversaturated reds on the skirt)

 

Custom LUT

[PannySVHS]

I built a set lut for an arri amira project. it has a nice look to it under uv, ir and various other outdoor lighting situations. Now I have been using my own flashy lut for other projects with Mavo LF and Lumix S Vlog material and it is neither accurate nor keeps colours intact. But interesting enough desaturating before and after the grading pipeline gives it back its integrety. Color correction within the node workflow gives it back its plausibility, keeping character and beauty, which this lut was built for as well. That in 70% of the cases. For 8bit Slog2 on the FS700 it did not work well at all.:) Oversaturated reds and blues was the problem.

I did a handcurve once for SLog2 material, which beat everything I was able to achieve with the official lut or CST. So I am always open for different ways.

What do you mean by curve before Gamut? Do you mean a separate gamma transform and a separate gamut tranform? How do you do that? @hyalinejim Awesome post btw. Thank you!

[hyalinejim]

On 1/13/2023 at 12:02 AM, PannySVHS said:

What do you mean by curve before Gamut? Do you mean a separate gamma transform and a separate gamut tranform?

Yes, you can isolate one or the other!

If you wanted to isolate Panasonic's offical VLog to V709 gamma (or gamut) you can use the excellent free online tool LutCalc (make sure Input Range and Output Range is set as below):

 

But I find Panasonic's V709 curve to be too mild: blacks don't reach the top and bottom of the waveform and middle grey stays annoyingly at 42 IRE instead of 49 where it "should" be:

 

In Resolve you can use the Color Space Transform effect. This is what it would look like for VLog to Rec709.

These settings would blow the highlights, though:

 

So I like this modification of the settings:

 

This gives a decent curve with dark blacks and middle grey at the right value:

 

Or, of course, you can use a simple RGB curve to create your own gamma curve, as you did for SLog2.

But regardless of which method you use, if you're separating the gamma and gamut transforms then the order in which they're applied is very important. In the case of Panasonic's transforms, if the gamma comes before the gamut then the colours will break. For Resolve's transforms, if you put the gamut before the gamma then the colours will be a bit inaccurate.

It's interesting to me because it's the Wild West out there in terms of what people are doing. I definitely think that some major YouTubers are doing things the "wrong" way, for example simply adding a curve to out of the box log footage and not transforming the gamut. Of course, if you like the results it doesn't really matter.

[TomTheDP]

Would be interested to hear your findings with Emotive colors LUT. 

Things like this is why it's nice to shoot ARRI, although like you said simply shooting RAW on any camera would at least give you the data to get you where you want to go without artifacts. 

[Kubrickian]

This guy does some great grading on VLOG. 
 

 

[PannySVHS]

@hyalinejim Cool thing, that is, being able to pick them without the other. Btw, my handmade SLog Curve with saturation and rgb curves adjusted was my last resort for some shots in 8bit SLog2 from the Sony A7sii. It was a camera with a rather lackluster implementation of Slog.:)

[MrSMW]

This is my next project.

I used to shoot the Natural profile before switching to Flat last year.

Now we are getting decent AF, I don’t need to make the same workaround choices (shooting more contrasty than log profiles, APSC crop, smaller apertures) so am intending shooting log this year mainly for the increased DR.

I will probably just stick with using FilmConvert Nitrate…

[TomTheDP]

9 hours ago, MrSMW said:

This is my next project.

I used to shoot the Natural profile before switching to Flat last year.

Now we are getting decent AF, I don’t need to make the same workaround choices (shooting more contrasty than log profiles, APSC crop, smaller apertures) so am intending shooting log this year mainly for the increased DR.

I will probably just stick with using FilmConvert Nitrate…

My suggestion with LOG is just to expose 1-2 stops over, just using the cameras light meter and then nail WB of course. I like Filmconvert a lot 

[MrSMW]

22 minutes ago, TomTheDP said:

My suggestion with LOG is just to expose 1-2 stops over, just using the cameras light meter and then nail WB of course. I like Filmconvert a lot 

That was/is my plan!

Thanks Tom

[markr041]

34 minutes ago, TomTheDP said:

My suggestion with LOG is just to expose 1-2 stops over, just using the cameras light meter and then nail WB of course. I like Filmconvert a lot 

Doesn't shooting overexposed reduce the dynamic range? It used to be necessary with the older sensors because of noise (shooting Slog2 or Slog3). It is no longer recommended for the newer Sony cameras precisely because it sacrifices dynamic range.

[TomTheDP]

1 minute ago, markr041 said:

Doesn't shooting overexposed reduce the dynamic range? It used to be necessary with the older sensors because of noise (shooting Slog2 or Slog3). It is no longer recommended for the newer Sony cameras precisely because it sacrifices dynamic range.

I don't shoot Sony. But I always over expose regardless of camera RED, ARRI, Panasonic, etc.. All cameras generate noise, if you want a clean image you overexpose, same goes for film. On RED or ARRI I just shoot at like 200 iso. ISO on the Panasonic in log is fixed though. 

If you like a bit of noise base exposure works. I personally do like grain so I sometimes will even shoot at say 1600 iso on ARRI to bring that out. For most stuff I assume people want it as clean as possible though. I also just don't think Panasonic looks as nice in the shadows. 

You don't really need to overexpose in very bright conditions but if you in a high contrast or low light situation its great. 

[markr041]

2 hours ago, TomTheDP said:

I don't shoot Sony. But I always over expose regardless of camera RED, ARRI, Panasonic, etc.. All cameras generate noise, if you want a clean image you overexpose, same goes for film. On RED or ARRI I just shoot at like 200 iso. ISO on the Panasonic in log is fixed though. 

If you like a bit of noise base exposure works. I personally do like grain so I sometimes will even shoot at say 1600 iso on ARRI to bring that out. For most stuff I assume people want it as clean as possible though. I also just don't think Panasonic looks as nice in the shadows. 

You don't really need to overexpose in very bright conditions but if you in a high contrast or low light situation its great. 

We understand the gain from ettr, I am just pointing out it comes with a cost, which is reduced dynamic range. The point is that overexposing is not always the best procedure, sometimes especially in a high contrast situation because of the reduced dr. One has to experiment, and results will also vary by camera.

[TomTheDP]

21 hours ago, markr041 said:

We understand the gain from ettr, I am just pointing out it comes with a cost, which is reduced dynamic range. The point is that overexposing is not always the best procedure, sometimes especially in a high contrast situation because of the reduced dr. One has to experiment, and results will also vary by camera.

It's my advice after years of owning and using the camera over many projects. For weddings there isn't a lot of time to deliberate on precise exposure, especially since REC709 monitoring is trash on Panasonic. Unless you are doing a silhouette shot it is what I would advise. I don't think I have ever been let down using this method. 

If you are used to shooting and exposing for the rec709 profiles on the Lumix I don't think you'll like log at base exposure. Personal preference of course just my advice. 

[Michael S]

On 1/17/2023 at 7:26 PM, markr041 said:

Doesn't shooting overexposed reduce the dynamic range? It used to be necessary with the older sensors because of noise (shooting Slog2 or Slog3). It is no longer recommended for the newer Sony cameras precisely because it sacrifices dynamic range.

When people say you must overexpose vlog by 2 stops, they mean the exposure meter must say +2. The reason for this is that the exposure meter assumes a standard gamma curve and not a log curve. As mid gray on a log curve sits two stops above mid gray compared to a normal gamma curve, the exposure meter must say +2. In my opinion this is a user interface design error from Panasonic which only leads to confusion. So the proper answer is that you must expose correctly, and therefore ignore the exposure meter when shooting in vlog. Use the spot meter (which switches to EI in vlog) or waveform. Spot meter must say +0 EI and mid gray on the waveform sits on 42%.

[hyalinejim]

2 minutes ago, Michael S said:

When people say you must overexpose vlog by 2 stops, they mean the exposure meter must say +2.

That's a very good point. I know from my own experience that V-Log on the GH5 metered -1 stop compared to the regular profiles, in line with what you're saying. On the GH6, however, that behaviour has been fixed and now 0 on the meter in V-Log is the same as in other profiles.

I don't know about other Panasonic models or cameras from other manufacturers.

[Michael S]

14 hours ago, hyalinejim said:

I don't know about other Panasonic models or cameras from other manufacturers.

I would have sworn I have seen the exposure meter on my S5 jump up and down when switching between vlog and the standard profile but as I checked recently, it now also stays fixed on 0. I wonder if it is one of those things they also silently fixed during one of the firmware updates. Or the fix accidentally got included as it is part of a common code base that gets shared between all models. Anyway, it behaves properly now on at least the S5.

[TomTheDP]

21 hours ago, Michael S said:

When people say you must overexpose vlog by 2 stops, they mean the exposure meter must say +2. The reason for this is that the exposure meter assumes a standard gamma curve and not a log curve. As mid gray on a log curve sits two stops above mid gray compared to a normal gamma curve, the exposure meter must say +2. In my opinion this is a user interface design error from Panasonic which only leads to confusion. So the proper answer is that you must expose correctly, and therefore ignore the exposure meter when shooting in vlog. Use the spot meter (which switches to EI in vlog) or waveform. Spot meter must say +0 EI and mid gray on the waveform sits on 42%.

Very interesting. Very bizarre mistake by Panasonic if that is the case with the S1. 

[MrSMW]

First attempt at grading Vlog.

Well first proper attempt and with the S5ii because I have tried in previous years with the S5 and S1H and always ended up going back to first the Natural profile and then the Flat profile.

This was with Gamut's (old, I need to download the latest version) re709 conversion and then my grade on top.

4k 50p S35 crop footage shot with Sigma 18-50mm f2.8 APSC lens.

[FHDcrew]

21 minutes ago, MrSMW said:

First attempt at grading Vlog.

Well first proper attempt and with the S5ii because I have tried in previous years with the S5 and S1H and always ended up going back to first the Natural profile and then the Flat profile.

This was with Gamut's (old, I need to download the latest version) re709 conversion and then my grade on top.

4k 50p S35 crop footage shot with Sigma 18-50mm f2.8 APSC lens.

This looks great!  Nice use of natural light too!

[MrSMW]

7 hours ago, FHDcrew said:

This looks great!  Nice use of natural light too!

Ha! Absolutely zero thought or planning just ‘stand there a sec, look left, look right, walk towards me’, just so I had a single piece of log footage to play with.

A lot of work to do you and then I’ll make a lut from whatever end grade I come up with for the stills work that is always the other 50% of the equation.

But thanks for the kind words 👍